Intertube intermediate-frequency coupling system



Jan. 20, 1942.

L. R. MLLING l INTERTUBE INTERMEDIATE-FREQUENCY COUPLING SYSTEM FiledApril 18, 1940 INVENTOR EONARD R. MALLING ATTORNEY ssuodsag ssuodssuPatented Jan. 20, 1942Y nv'rnn'runn murmura-FREQUENCY j.

coUruNG srs'rmu Leonard R.. Mailing, Dougiaston, N. Y., assignor toHazeltlne Delaware Corporation, a corporation of LApplicmxnm April18,1940, serial No. 330,278

(ci. usp-111) l Claims.

This invention relates generally to intertube intermediate-frequencycoupling systems for modulated-carrier signal receivers and particularlyto such coupling systems 4suitable for use in television signalreceivers.

It is frequently desirable to provide an inter-v tubeintermediate-frequency coupling system for a modulated-carrier receiverwhich includes a double-tuned selector circuit and means for modifyingthe response of the coupling system at a fixed frequency outside of, butadjacent to, the normal pass band of the selector. For instance, a trapcircuit fixed-tuned to an undesired signal has been utilized in serieswith one of the windings of such a double-tuned selector to providesubstantially infinite attenuation of such undesired signal. However,when a receiver including such a coupling system is to be constructed inaccordance with the usual production methods, it is necessary to providesome way of adjusting the pass-band characterlstic of the otherreceivers which operate at a relatively high frequency to add anycapacitance to the circuit. At the same time, it is desirable to providea coupling system of the type under discussion, the band-passcharacteristics of which can be adjusted without affecting undesirablythe operation of a trap circuit associated with the selector.

It is well known, of course, that the band-pass characteristics of adouble-tuned selector circuit, can `be adjusted by varying the mutualinductance between the windings of the selector circuit. However, ingeneral, vthis has the effect of adjusting the band-pass characteristicsof the selector symmetrically, -thus undesirably impairing theselectivity of the selector at the cutoi frequency other. than thatbeing adjusted, and at the same time modifying the operation of a trapcircuit associated with the band-pass selector. ForV this reason, thismethod of adjusting the band-pass characteristics of doubletunedselector circuits of the prior art to align th'e coupling system of suchtype with other selective circuits in a modulated-carrier signalreceiver has not been satisfactory. I-t is, therefore, very desirable toprovide a coupling system of the type under discussion in which thesediiliculties are not present. Also, in television systems, intertubeintermediste-frequency coupling systems have been utilized whichcomprise a double-tuned band-pass selector effective to translate thevision intermediate-frequency signals. However, in television systemsthe sound intermediate-frequency signals are conventionally transmittedon a carrier wave closely adjacent the frequency band within which thevision signals are transmitted. It is, therefore, frequently desirableto increase the response of an intertube intermediate-frequency couplingsystem, which includes a double-tuned band-pass selector for translatingvision intermediate-frequency signals, at the frequencies occupied bythe associated sound signals. If a tuned circuit is used for thispurpose, it should be resonant at the intermediate-carrier frequency ofthe sound signals. However, the same diillculties mentioned above arepresent in an arrangement of this type; namely, it is diiilcult toadjust the band-pass characteristics of the double-tuned selectorcircuit provided for translating the vision signals so that the circuitis correctly aligned with other selective circuits of a televisionreceiver without adding additional capacitance to the circuit. Also, ifthe mutual inductance of such a double-tuned band-pass selectorisadjusted to procure alignment, the response of th'e tuned circuitprovided to secure increased response to sound signals is changed,unless special precautions are taken which have :is nio; hitherto beenknown to those skilled in the y It is an object of the invention,therefore, to provide an intertube intermediate-frequency couplingsystem of the type under discussion in which the mutual inductance of adouble-tuned selectorV circuit can be varied to align the circuit withother selective circuits of a receiver without substantially affectingthe frequency of maximum response of a resonant circuit associated with'one of -the windings of the doubletuned selector circuit.

It is a further object of the invention to provide an intertubeintermediate-frequency coupling `system including a double-tunedselector circuit having a trap circuit vconnected in series with one ofits windings in which vthe response characteristic of the selector canbe adjusted without varying substantially the effect of the trapcircuit.

It is a further object of the invention to provide, in a superheterodynereceiver including an intertube intermediate-frequency channel adaptedtc translate vision intermediate-frequency signals and associated soundintermediate-frequency signals, a double-tuned selector circuiteffective to translate the vision intermediate-irequency signals andhaving in series with one of the windings thereof a parallel-resonantcircuit eective to accentuate the response of the system to the soundintermediate-frequency signais, in which the mutual inductance betweenmediate-frequency signal, a substantial part of the capacitance beingthe inherent capacitance of the circuit and associated tubes. In apreferred embodiment of the invention, the capacitance isv whollycomposed of the inherent capacitance of the tubes and circuits of theselector. A parallelresonant circuit is also coupled in series with oneof the windings to modify the response of the coupling system primarilyat afrequency outside of, but adjacent to, the desired pass band of theselector, the parallel-resonant circuit comprising capacitance of avalue greater than ten times that of the above-mentioned capacitance.Means are further provided for adjusting the mutual inductance betweenthe windings to adjust the coeilcient of coupling of the transformerwithin a range of i 10% thereby to adjust the band-pass characteristicsof the selector without substantially altering the response of thecoupling system due to the above-mentioned parallel-resonant circuit. 1

In a preferred embodimentof the invention, the parallel-resonant circuitis a trap circuit included in series with the primary winding of thetransformer to provide high attenuation against undesired signals on anadjacent channel. Also, in accordance with a preferred embodiment of theinvention, the receiver is a television receiver adapted to transmitvision intermediate-frequency signals and associated soundintermediatefrequency signals and the above-mentioned bandpass selectoris adapted to translate the vision intermediate-frequency signals. Inthis embodiment of the invention, the parallel-resonant circuit may becoupled in series with the secondary winding of the coupling transformerand utilized to increase the response of the coupling system at thefrequency of the sound intermediate-frequency signals, thus rendering atleast a portion of the separate sound intermediate-frequencyamplification usually provided unnecessary.

Also in accordance with a `feature of the invention, anintermediate-frequency signal-translating channel for a televisionreceiver includes a plurality of intertube coupling systems coupled ,Yin cascade, each of which comprises, a transformer includingclosely-coupled primary and secondary windings individually adapted to.be tuned by capacitance to form a band-pass selector for passing visionsignals of a wide frequency range, the capacitance being wholly composedof the inherent capacitance of the circuits and the tubes to which thewindings are coupled, and means for aligning the coupling systemscomprisingly solely means for adjustably fixing the mutual inductancebetween the transformer windings. By this arrangement the couplingsystems can be aligned with each other and the overall-response of theintermediate-frequency coupling system can be adjusted to transmit witha uniform amplitude a desired wide band of picture signals.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawing and itsscope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a circuit diagram, partly schematic, of acomplete television signal receiver system including anintermediate-frequency coupling system in accordance with the presentinvention, while Figs. 2 and 3 comprise graphs utilized to explain theoperation of a portion of the circuit of Fig. 1.

Referring now more particularly to Fig. 1 of the drawing, the receiverthere illustrated comprises a television receiver of the superheterodynetype including an antenna system III, II connected to a radio-frequencyamplifier I2 to which are connected in cascade, in the order named, anoscillator-modulator I3, a vision-signal and sound-signalintermediate-frequency amplitler I4, a vision-signal and sound-signalintermediate-frequency amplifier I4', an intermediatefrequency amplifierand vision-signal and sound-k signal separator I5, a vision-signaldetector and.

AVC supply I6, a video-frequency amplifier II, and an image-reproducing.device I8, forexample, a cathode-ray signal-reproducing tube. Alinescanning generator I9 and a field-scanning generator 20 are alsocoupled to the output of detector I6 through a synchronizing-signalseparator 2| and to the scanning elements of the imagereproducing deviceI8. In order to provide sound reproduction in the receiver shown, thereis coupled to intermediate-frequency amplifier I5, a sound-signalintermediate-frequency amplifier 22, to which is coupled in cascade, inthe order named, a sound-signal detector 23, an audio-frequencyamplifier 24, and a sound-reproducing device 25. A bias is derived fromunit I6 and applied over the conductor marked AVC to one or more of thetubes of stages I2-I5, inclusive, to control the amplification thereofinversely in accordance with the received signal strength. The stages orelements III-25, inclusive, excepting amplifiers I4 and I4 constitutingthe present invention and presently to be described, may all be ofconventional well-known construction so that detailed illustrations anddescriptions thereof are unnecessary herein. f

Referring briefly to the operation of the system just described, soundand vision modulatedcarrier signals intercepted by the antenna circuitI, II are selected and amplified in the radio-frequency amplifier I2 andsupplied to the oscillator-modulator I3 wherein they are converted tointermediate-frequency signals which,`

in turn, are amplified in intermediate-frequency amplifiers I l and I4'.The signal output of amplifier I4 is further amplified in amplifier I 5,from which vision intermediate-frequency signals are delivered todetector I6. 'I'he modu-V lation components of this signal are derivedin 2,270.51 j 3 In order to modify the response of the coupling thedetector i3 and are supplied to the video= frequency ampliiier 1,wherein they are amsystem of the invention primarily at a iixedfrepliiied and from which they are applied to a" brightness controlelemento! image-reproducing quency outside of, but adjacent to, thenormal pass band of the selector, and specifically in order device I3.Theintensity of the scanning beam -5 to provide a trap circuit effectiveto provide ahigh of device I3 is thus modulated or controlled inaccordance with the video-frequency voltages impressed on its controlelectrode in "the usual manner. A control-bias voltage developed by theAVC supply Il and proportional to the averlo age vision-carrieramplitude and independent oi its modulation components'is supplied inthe usual manner to the control grids of tubes in one or more of thestages |2- I5, inclusive, for

maintaining the signal input to detector I3 with- 15 in a relativelynarrow range for a wide range of received signal intensities.

'I'he modulation signal output of detector I6 is also applied tosynchronizing-signal separator 2| from which suitablesynchronizing-signal go components of the signal are supplied tovlinescanning generator I3 and field-scanning' generator to synchronizethe operation of these circuits with corresponding apparatus at thetransmitter. Saw-tooth current or voltage scanning waves are developedby generators |3 and 2li and these waves are applied to the scanningelements of device I3 to produce scanning fields, thereby to deiiect thescanning beam in two directions normal to each other so as to trace suc-3 cessive series of parallel lines or fields on the target of theimage-reproducing device' I3 toreconstruct the image. Soundintermediate-frequency signals derived from amplifier I3 'are furtherampliiied in sound intermediate-freplanation of the operation of theportion of the quency amplifier 22and delivered to detector 23, whereinthe audio-frequency components are derived. These components are, inturn, ampliiied by audio-frequency ampliiier 2l and deattenuation ofundesired Signals on such nxed provide an increased response for theassociated sound intermediate-frequency signals, there isv provided aparallel-resonant circuit 33, 43 connected in series withsecondarywinding 34. Means indicated by an arrow are provided for adjustablyfixing the mutual inductance between the windings 33, 3l. Trap circuitsl4| and `l2 are Y included in the cathode circuits 'of tubes and 3|,respectively, to provide increased attenuation lof undesirable signalson adjacent channels.

"cn-cunts u anun as wen as circuits s1, :a and 33, 30 are preferablytuned by means of an adjustably-iixei magnetic core in'the inductanceelement of the circuit, the capacitance element in each case being xed.It will be understood that there may also be included in ampliiier I4anintermediate-i'requency coupling system identical with that oiamplifler Il and that units Il and- II',- therefore, provide a pluralityof similar intertube coupling systems coupled in cascade. Y

Reference is made to Figs. 2 and 3- forl an ex- -A the desiredfrequency-response characteristicof the band-pass selector, per se', ofthe interlivered to sound-reproducing device 25 for re- 4mediatfrequency coupling System of the inproduction in a conventionalmanner. The AVC bias derived from AVC supply source I6 and apy plied tostages |2|5, inclusive, also serves tomantain the signal inputtodetector 23 within vention. 'I'his response characteristic extends overa broad frequency range including a frequency range f1, fz over which itis desired to Y procure -a relatively high and uniform responserelatively IlarlOW limits fOr 8 Wide range 0f lea by means ofthedouble-tuned band-pass selector ceived signal intensities.

Referring now more particularly to the portion of the system of Fig. Iembodying the present invention, there is provided an intertubeintermediate-frequency coupling system for a modulated-carrier signalreceiver for coupling the output circuit of a vacuum tube 30 ofamplifier- I3' to the input circuit of a succeeding vacuum tube 3|. Itwill be understood that only the portions of the circuits of tubes 30and 3| neces- 55 sary for an explanation of the present invention areshown in detail and that the other necessary portions of these twocircuits may be in accordance with conventional design. Theintermediate-frequency coupling system of the inven- 0 tion comprises atransformer including closelycoupled primary and secondary windings 33and 3l individually adapted to be tuned by the inherent capacitance ofthe circuit and of the tubes to which they are coupled to form abandpassselector for passing vision intermediate-frequency signals. The tuningcapacitances ofwindings 33 and 3l are indicated by the dotted-. linecondensers 35, 36 for the reason that these capacitances may becomprisedin whole or in circuit 33, 35 and 33, 36. The actual band-passcharacteristic of the circuit before an aligning operation has beenperformed'thereon may be of the form illustrated by dashed-line curve Bwhich comprises resonance peaks in the response characteristic which arewidely separated in frequency. The band-pass characteristic of thecircuit after the mutual inductance between windings 33 and 34 has beenadjusted to procure the desired response over the frequency range f1, l:is illustrated by the curve C, and is preferably such that the doublepeaks thereof are outside of the frequency range f1, fr. If -ampliiierllalso comprises an identical coupling system, its responsecharacteristic may be aligned in a similar manner.

'I'he desired over-all response characteristic of the coupling system ofthe invention or of a vplurality of such coupling systems coupled incascade is illustrated in Fig. 3. The curve of Fig. 3 comprises aportion of'increased response at a frequency f3 which is thecarrierfrequency of the intermediate-frequency sound signals associated withthe vdesired intermediate-frequency sound signals.- this increasedresponse being due to the parallel-resonant circuit '33, Il which isresonant at the carrier frequency of the intermediate-frequency soundsignals. The curve of Fig. 3 also has a high attenuation at'a frequencyf4 which is due to theV trap circuit 31, 33

trated in Fig. 1, it is usually found that, due to variations in theelectrical constants of the elements which are assembled to produce thecoupling system -and variationv of inherent wiring inductance andcapacitance, the desired response characteristic illustrated by curve Aof Fig. 2 is not obtained. Specifically, in the example chosen forillustration, the response characteristic of curve B may be obtained.Y'I'he procedurein procuring the desired over-all nesponsecharacteristic may be as follows: the desired maximum response in theover-all coupling characteristic illustrated in Fig. 3 at frequency f3may be first procured Aby adjustably fixing the inductance of inductor40 to tune the resonant circuit 33, 43 to the frequency fa andthereafter inductor 33 may be adjustably fixed to tune the resonantcircuit 31, 38 to the frequency f4, thereby to procure maximumattenuation at frequency f4. If an attempt is then made to procure thedesired over-all band-pass characteristic from the system by means ofadjustment of trimmer condensers or other means used in prior artarrangements, it is found that the frequency of increased response f3and the frequency of maximum attenuation ,f4 tend to vary with suchadjustments.

Therefore, in accordance Vwith one feature of the present invention, theL/C or inductance-tocapacitance ratio of the parallel-resonant circuits31, 33 and 33, 40 is designed to benly a small fraction of that of theresonant circuits 33, 35 and 34, 36 in series with which they arerespectively connected. Under these conditions the mutual inductancebetween windings 33 and 34 maybe adjusted over a range sufficient toadjust the coefficient of coupling over a range of i-10% to cause theband-pass characteristic of selector 33, 35 and 34, 36, assumed to berepresented by curve B to be broadened, as illustrated by curve C toinclude the range f1, fz within the portion over which it has a. maximumand substantially uniform response. This adjustment has substantially noeffect upon the over-all response 'characteristic represented in Fig.' 3at the fre-` quency of increased response f3 or at the frequencyresponse of maximum attenuation f4. In other words, if theparallel-resonant circuits 31,' 33 and 33, 40 individually comprisecapacitances of a value of the order of, or greater than, ten

times that of the capacitances 35 and-36, respectively,the circuit ofthe invention may be aligned with other selector` circuits of thereceiver by adjustment of the mutual inductance betweenwindings 33 and34 without substantially altering the response of the coupling systemdue to the parallel-resonant circuits 31, 33 and 39, 40. At the sametime the over-all selectivity is not impaired at the cutoff frequenciesdue to the effect of tuned circuits 31, 33 and 33.43.

It will be understood that, while parallelresonant circuits 31, 33 and39, 40 have been shown as being connected to the low signalpotentialterminals of windings 33 and 34, respectively, these parallel-resonantcircuits may be connected to the high signal-potential windings of theirrespective circuits and that certain of the benefits of the inventionstill will be procured. However, if the parallel circuits are con-`coupling system similar to that of amplifier I 4 andhaving a band-passselector response characteristic as illustrated by curve B of Fig...2,it can also be properly aligned by means comprising solely means foradjustably fixing the mutual inductance between the transformer windingsin the manner just described.

. While there has been described what is at present considered to be thepreferred embodiment of this invention, it will be obvious to thoseskilled in the artl that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true-spirit and scope of the invention.

What is claimed is: l l. An intertube intermediate-frequency couplingsystem for a modulated-carrier signal receiver comprising, a transformerincluding closely-coupled primary and secondary windings indivlduallyadapted to be tuned by capacitance to form a band-pass selector forpassing a wide band intermediate-frequency signal, .a substantial partof said capacitance being the inherent capacitance ofthe circuits andthe tubes to which the system is coupled, a parallel-resonant circuiteffectively in series with one of said windings to modify the responseof said coupling system primarily at a frequency outside of, butadjacent to, the desired pass band of said selector, saidparallel-resonant circuit comprising capacitance of a value greater thanten times that of said firstmentioned capacitance, and means foradjusting the mutual inductance between said windings to adjust thecoecient of coupling of said transformer within a range of i 10%therebyto adjust the band-pass characteristics of said selector withoutsubstantiallyv altering the response of said coupling system dueto saidparallel-resonant circuit.

2. Anintertube intermediate-frequency coupling system for amodulated-carrier signal receiver comprising, a transformer includingclosely-coupled primary and secondary windings individually adapted tobe tuned by capacitance to forma band-pass selector for Vpassing a wideband intermediate-frequency signal, said capacitance being composedwholly of the inherent capacitance of the circuits and the tubes towhich the system is coupled, a parallel-resonantcircuit effectively inseries with one of said windings to modify the response of said couplingsystem primarilyat a frequency outside of, but adjacent to, the desiredpass band of said selector, said parallel-resonant circuit comprisingcapacitance of a value greater than ten times that of saidfirstmenticned capacitance, and means f'or adjusting the mutualinductance between said windings to adjust the coeiiicient of couplingof said transformer within a range of thereby to adjust the band-passcharacteristics of said selector without substantially altering theresponse of said coupling system due to said parallel-resonant circuit.

3. An intertube intermediate-frequency coupling system for a televisionreceiver adapted to translate -both sound and visionintermediatefrequency signals comprising, a transformer includingclosely-coupled primary and secondary windings individually adapted tobe tuned by capacitance to form a band-pass selector for passing visionsignals of a wide frequency band, said capacitance being wholly composedof the inherent capacitance of the circuits and the tubes to which thesystem is coupled, a parallel-resonant circuit effectively in serieswith said secondary windingto increase the response of said couplingsystem4 primarily at the carrier frequency of said soundintermediate-frequency signals, said parallel-resonant circuitcomprising capaciresponse of said coupling system due to saidparallel-resonant circuits.

6. an intertube intermediate-frequency coupling 'system for amodulated-carrier receiver comprising, a transformer includingclosely-coupled primary and secondary windings individualv ly adapted tobe tuned by capacitance to' form a band-pass selector for passing a,wide band intermediate-frequency signal, said capacitance being whollycomposed of the inherent capacitance of the circuits and the tubes to.whichv the system is coupled, and a parallel-resonant circuit tance ofavalue greater than ten times that of said mst-mentioned capacitance, andmeans for adjusting the mutual inductance between said windings toadjust the coefficient of coupling of saidtransformer within a range of`\i f10% thereby to adjust the band-pass characteristics of saidselector without substantially altering the tenuate theresponse ofisaidcoupling system primarily at a fixed frequency of .an undesired signaloutside of, but adjacent to, the desired pass band of said selector,said parallel-resonant circuit. `comprising,capacitance of a valuegreater than ten times that of said rst-mentioned .capacitance, andmeans for adjusting the mutual inductance between said windings toadjust the coeicient of coupling of said transformer within a range ofthereby to adjust the band-pass characteristics of said selector withoutsubstantially altering the response ofv said coupling system due to saidparallel-resonant circuit.

5. An intertube intermediate-frequency coupling system for amodulated-carrier receiver adapted to translate associated vision andsound intermediate-frequency signals of a television signal comprising,a transformer including closely-coupled primary and secondary windingsindividually adapted to 'be tuned by capacitance to forma band-passselector for passing a wide band intermediate-frequency vision signal,said capacitance being wholly composed of the inherent capacitance ofthe circuits and the tubes to which ghe system is coupled, aparallel-resonant circuit effectively in series with said primarywinding to attenuate the responseof said cou'- pling system at afrequency corresponding to the sound intermediate-carrier frequency ofan adjacent television signal, and a parallel-resonant circuit coupledin series with said secondary winding to increase the response of saidcoupling system primarily at the intermediatecarrier frequency of theassociated sound signals, said parallel-resonant circuits eachoomprisingcapacitance of a value greater than ten times that of said mst-mentionedcapacitance, and means for adjusting the mutual inductance between saidwindings to adjust the coeicient of coupling of said transformer withina range of il0% eilectively in series with the low-potential ter- .minalof one of said windings to modify the respouseof lsaid coupling systemprimarily at a frequency-outside of, but adjacent to, the desired passband of said selector, said parallelresonant circuit comprisingcapacitance of a value greater than ten times that of saidilrstmentioned capacitance, and means for adjusting the mutualinductance between said windings to adjust the coefficient of couplingof said-transformer vwit-hin a range of :10% thereby to adjust theband-pass characteristics of said selector without substantiallyaltering the response oi said coupling system due to said parallel-reso-7. An intermediate-frequency signal-translating channel for a televisionreceiver including a pluralityof intertube coupling systems coupled incascade, each of which comprises, a transformer includingclosely-coupled primary and secondary windings individually adapted tobe tuned by capacitance to form a band-pass selector for passing visionsignals of a wide frequency range, said capacitance being whollycomposed of the inherent capacitance of the circuits and the tubestowhich the system is coupled, a parallel-resonant circuit effectivelyin series with one of said windings to modify the response of saidcoupling system primarily at a frequency outside of, but adjacent to,the .desired pass band of said selector, said parallel-resonantcircuitcomprising capacitance of a value greater than ten times that ofsaid first-mentioned capacitance, and; means for adjustably fixing themutual inductance between said windings to adjust the coeillcient ofcoupling of said transformer within a range of :10% thereby to adjustthe band-pass characteristics of said selector without substantiallyaltering the response of said coupling system due to saidparallel-resonant circuit.

8. An intermediate-.frequency signal-translating channel for atelevision receiver including a thereby to adjust the band-passcharacteristics plurality of intertube coupling systems coupled incascade, each of which comprises, -a transformer includingclosely-coupled primary and secondary windings individually adapted tobe tuned by capacitance to form a vband-pass selector for passing visionsignals of a wide frequency range, said capacitance being whollycomposed of the inherent capacitance of the circuits and the tubes towhich said windings are cc upled, and means for 'aligning said couplingsystems comprising solely means for adjustably xing the mutualinductance between said windings, whereby said coupling systems can bealigned with each other and the over-all response of saidintermediate-frequency coupling system can be adjusted to transmit witha uniform amplitude a desired wide band of picture signals.

9. An intermediate-frequency coupling system for a television receiverincluding a plurality of intertube coupling systems coupled in cascade,each of which comprises, a transformer including primary and secondarywindings having a coeiilcient of coupling therebetween of over 40% andindividually adapted to be tuned by capacitance to form a band-passselector for passing vision signals, said capacitance being whollycomposed of the inherent capacitance of the' circuits and the tubes towhich said windings are coupled, and means `for aligning said couplingsystems comprising solely means for adjustably ilxing the mutualinductance between said windings to vary the coemcient of couplingbetween said windings over a range of :10%, whereby said. plurality ofintertube coupling systems can be aligned to pass a predetermineddesired band of frequencies with a substantially uniform response.

l0. An intermediate-frequency coupling sys-` tem for a televisionreceiver including a plurality of intertube coupling systems coupled incascade.

each of which comprises. a transformer including closely-coupled primaryand secondary windings individually adapted to be tuned by saidcapacitanceto form a band-pass selector for passing vision signals of awide frequency range. said band-pass selector having resonance peaks jinits response characteristic which are widely separated in frequency, andsaid capacitance being composed wholly of the inherent capacitance ofthe tube circuits in which said windings are coupled, and means foraligning said Icoupling systems comprising solely means for adjustablyxing the mutual inductance between said windings to adjust saidintertube coupling systems to pass a relatively wide band of frequenciesbetween said resonance peaks with substantially uniform response.

- LEONARD R. MALLING.

